Ignition control



Aug. 24, 1948.

P. W. PRATT IGNITION CONTROL Filed oct. 27. 1945 2 sheets-sheet 1 METER/Na cna/v ATTORNEY.

Aug. 24, 1948.

Filed 001;. 27, 1945 B'Sheets-Sheet 2 `ATTORNEY.

patented ug. 24,1948

`IolizrrlON CONTROL Perry W. Pratt, Manchester, Conn., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application October 27, 1945, serial No. 625,078

'This invention relatesto ignition timing systems, particularly for internal combustion aircraft engines.

j An object of this invention is to provide a simplication and improvement in engine ignition timing systems, particularly adapted for use with ignition timing systems of the type disclosed and claimed in Jarvis U. S. Patent No. 2,380,967.

Another object is to provide means for shifting an aircraft engine ignition timing device to both advanced and retarded spark positions by supercharger pressure rise.

n further object is to provide an improvement in the construction and arrangement of a spark advance control unit.

Other objects and advantages will be apparent from the specification" and claims, and from the accompanying drawing which lllustrateswhat is now considered to beV a preferred embodiment of the invention. y

Referring to the drawings, Fig. 1 is a diagrammatic View showing the actuating and control portions of an ignition timing system constructed according to the teaching of the present invention, and particularly adapted for use with a radiall aircraft engine having an engine driven supercharger.

Fig. 2 is a sectional viewl of the spark advance control unit taken` along the line 2-2 of Fig. 1.

Fig. 3 is a sectional view along the line 3--3 of Fig. 2. Y

Fig. 4 is a sectional view along the line 4--4 of Fig. 2,. 1 i

Fig. l5 Vis a sectional view along the line 5--5 of Fig. 4. i

Fig. 6 is a diagrammatic view showing a modie cation of the timing system of Fig. 1 ywhich is particularly adapted for use with a radial aircraft enginehaving a supercharger driven by the engine through a two-speed transmission and incorporating means for compensating `the operation of the control unit for changes in the speed ratioof the transmission. 5

Two preferred embodiments of this invention are described'below. The first (Fig. 1) utilizes to some extent the teaching of Jarvis U. S. Patent No.'l 2,380,967. The'second (Fig. 6) utilizes to some extent the teachings of Hasbrouck U S. application Serial No. 469,931, now Patent No. 2,390,146, filed Decemberv 23, 1942, Parkins et al.

U. S. application Serial No. 479,600, now Patent s claims. (ci. 12a-1117 Description of Fig. 1 This figure Ashows a portion of the fuel and air system for a radial 'aircraft engine including a 4 carburetor air metering section, a carburetor fuel carburetor (a portion of which is shown at 30) i and then to the. engine cylinders (not shown)` through the supercharger inlet-pipe 25. the supercharger or blower 22, and the induction pipes 24. Thesupercharger is preferably. Of a conventional type, having a centrifugal impeller (not shown) vmounted on an engine driven shaftf28. The rate of airflow is controlled in a conventional way by throttle 32, located in the intake passage upstream ofthe inlet to blower 22. A pair of venturis, one of` which is partially shown at 34, and

limpact tubes 50 establish a pressure difference stem 54.y Fuel is pumped to the engine cylinders by the fuel supply pump in an amount regulated in predetermined relation to intake airflow by valve 60. `Inf desired, this valve may be biased to open position by a Weak spring 6l and it is alsofurged to open position by the air` head force applied by'diaphragm 38 to stem 54. Fuel passing through valve 60 flows throughthe main metering jet or `flow restriction'l of the fuel No.'2,39o,166, niet Meren is, 1943, and Waring U. S. application Serial No. 601,437, filed June 25, 1945, all assigned to applicant's assignee.

metering section and then passes tothe engine through the` fuel conduit 14. Additional fuel may be admitted to the engine` at higher engine outputs, `in `a known` manner, by economizer valve 80. .The fuel ow through jet 'l0 is preferably controlled to provide rich or lean fuel-air ratios, ormixture settings, by mixture control valve 18. Under idling conditions the fuel flow maybe regulated by the idle valve |51.

Fuel flowing through jet 10 (and at higher engine powers through economizer valve establishes a fuel head differential on opposite sides of a fuel diaphragm 58 attached to fuel valve stem 54. This fuel head is a measure of the rate of fuel llow by weight and exerts a resultant force on diaphragm 58 and stem 54 which urges valve 60 to closed position. Consequently diaphragms 38 and 58 cooperate to position valve 60 so as to proportion the fuel flow and airowvin predetermined ,ratio which, rati o may be controlledby the valves '|81 and {80?1' It will be further seen that the y'fuel"l'1e`ad across 10 diaphragm 58 between the unmetered fuel cham?,4

0r pressure diierential acrossuairdiaphragm Lilli.:

Therefore the fuel metering'differeiitial, alsgwe x as the air differential, is an accurate measure of intake airow and engine pwrfand may be'l utilized for actuating the spark advance ..control power.

The ignition timingoperating unit and timing adjustment mechanism are alsodescribedirLdQ- taili'n lJ'ar vji `s U; S.' 'Patent No. 2 ,"3'80,96' 7."f The pp erating' unit in'liides f alfchamb erf 'I 10 1 which con; 25

saine, as di s cl"o s"edf V in the Jarvis patent.' 'the '1, positioniof the operating unit shown 1inA Fig. 1',

' e 1152x120 `.lille/Nil) diaphragm is subjected to 'fuel metering pressurefco compression 'spring'Zll'S arid'is rapidly movedtq' 70 its? extreme fright' hand' y,the liueif.l head "across tdiapll'ragrh |854 increasesbeyond af predetermined valuewhch'is'sufiiciently larg'efto overcmetheffere f spring 20'65- operating gimit "the 50 4| tion as shown in Fig. 1 conduits |14 and |14' are interconnected by the valve channel |15 (Fig. 2) and the conduits I'IG, |16 are interconnected by the valve channel |11. In this position of the control unit (at low fuel metering heads and low engine power) the pressure rise directly across the supercharger is exerted on diaphragm |12 in adirectionterrding to urgestexndg ofthe operating; unit'.'dovyn wardly, to the spark advanced position. However, under engine idling conditions or at lower engine powers the supercharger pressure rise is quite low, because the supercharg'erimpeller will be rotating at relatively low speeds. Spring, |8. is made strong enough to overcome"thisgielatiyely lolw supercharger pressnreisend,consequently the stem |62 of the operating unit will be held in its upper, spark re- *cardedpositioiivbythel spring |18 for starting and `e`pressure rise across the supercharger is a fairly accurate, linc lication of, enginepower i and further'. 'Mendes' al flid Dresser@ 'diienieli which is ofsuficientsize-to provide ana mating, pressurefor the ignition, timingoperati g unit;

Therefore, when 'throttleaz is'ppened tqincreasq engine power 4the pressure, rise 1across the super:- charger also,.in lzieasegl b ecauseof the increasxed-v., impellerv spee d and wherithe' engine reaches app1oache's'-the cruising or; intermediate power range the pressure 'head.across diaphragm ,|'|2 becomes large enough tol'overcome ,theforge'fpff spring V18 and forces stem |`6 2` down wardly toits lowermost position. thereby, @needing .Commit i 50 lvjto drainl and connecting conduit I5 8 to the:

`idli gonditlons. unit in accordance with. variations inL engine' 20 'I' Vpressure source |52, thereby aqtuatingtli'e hift:

ing mechanisnrlI ,sowas tochaiighetljieignition timing to thesparkalvancedposition,

During uns; prjoess.; vali/@piston '9.0'. remains., in yits left` hand position because 'fthe spring, 2li@ Iis -'made strong enough 'to' overcomev the force.. exerted on ldiaphragm |8I i by, t'l 1 e fuel ynieizering diffrente?dirinadliriaaed Cruising. winter.; mediatepowersf- Wiifu'rthr .increases @engine Poweliuner.: charger' pressure rise alsof further inc i'ea'sesf ADia 'phrem' lf2 'arid' valve |62 wllihfelfore belmain tainedin the spark vadvanced fpos`itio r 1 untill (elle eine, Dover .approaches or wehe? ,thee fullo@ hiefelpowef range' brjueiil. theiuetmeteriee headj" across. .diaphragm f8.6 .increases beyond-,a

conduit I'Ito conduit |74, just/'they oppositejof'f 'theoonnections `described labove for the' left hand?r position of thevalvepiston.-

lWhen the z valve, piston isl .in ..the' righty hand -r position as shown in Figs;.fioanda5.-fthesLiper-.J` charger. Ioutlet;-l3l flSSurewillibe applied.;.by con.

'bhrgm .me .direction tendine tOEmOi/'eihe-ralre .th forc Offspring. |205.the@Pringleriscalda) control unit. A

designed so that this voccurs atithe u-pperfyendof; theY cruising lpower range), valve y|62 .o fthe operating .unitV will -be rapidlyv and.- positively ,moved upwardly by vsupercharger pressure rise. to the spark retarded position of Figl,A in which pressure oil is-admitted--irom line |52 lto the line `|60 to actuate theshifting mechanism IOI so as to change to the. spark retarded position. l s

Y openen-ny of-'Fiep 1 Under engine starting and idlinglcondltions: the control unit is maintained in the left hand position by springv206 and thev linesv |14, I 16 are vconnected to lines |14',v |16', respectively, thereby subjectingthe ftop of `c iiaphragm I' I2to supercharger outlet pressure and thev bottom of diaphragm |12 to supercharger inlet` pressure. However, spring |16 holds valve |62 in the spark retarded-position. "When the engine power isincreased to the cruising range the pressure diiferential between the supercharger outlet .and

inlet becomes large enough (such 'as -5' .Hg forr to the conduit I16f and connecting conduit |16 to conduit |16'. This reverses the pressure dii'-, f

ference across diaphragm |12, subjecting its lower side tosupercharg'er outletl pressure and its upper sideto fsuperchargen inlet pressure. This reversal of the iluidwpressureforce applied by the supercharger to the diaphragm |12 .positively shifts the operating valve |62. upwardly t0. the

position in which themechanism IOI shifts the spark tothe retarded position. Spring. |16 aids,I

the upward movement of valve |62. With this arrangement the supercharger pres-v surecrise moves the ignition timing operating unit toboth retarded and advanced positions. Yet:

the point or time at whichthe timing change ismade isfcontrolled very accurately according" to 'variations in fuelhead by the sparkadvance Description l of Fig. 6

rn the embodiment of this figure the superchargeris driven byV a gear transmission having a clutch face or friction band 26-4 thereon with which the clutch'element 266 may be engaged,

speed ratiodrive for the impeller `shaft 26. Gear 254 is provided with a similar band 266 which-is engaged by axial `movement of element 210 to form a highspeed ratiodrive.

`*Power is transmitted fromv the engine crank# shaft to the supercharger impelier through engine driven-tail shaft 36', the geart246 (which incorporates. .a aspring" drive @unit- 245) ,pinion 24|,

vposition shaft 250; either low speed1gear'252 orbigh speed gear '254 (depending upon which of the clutch elements 266, 210 is engaged) `and impeller shaft 28. v

Each clutch is urged toward disengaged. posi-V Athe cylinders or chambers 214, 216, respectively -BIS4 byfaidalV movement of vthe element along the splines on` the shaft 250, to form a relatively low` associated with each clutch. .The parts are so arrangedl that iluid admitted to -either chamber facts von the corresponding clutch element to move itaxially, like a piston, to compress the spring 212-and to engage. the clutch element with `the surrounding gear. Admission of uidto the chambers 216, 216 is controlledby valve 306, shown in thelow speed ratio` positionv in Fig. 6 with the low gear clutch 268,` 252 engaged.` When the` valve handle 306 and valve 306 are in the position shown in this Lgurailuid is admitted from thepressure source 2| 8 to the pipe 2 I5. From there it passes through the inner bore 04 to the low clutch Vchamber 21.4,V

where itforces element 268 into driving contact with band264 and engages the transmissionin low gear ratio, Vto drive the impeller atfa low.' speed `relative to engine speed. When pressure.

iluid is beingV admitted to pipe 2 I5 the high ratio clutch chamber 216 is connected to the drain 200, by bore |30 and pipe 2I3. Consequently spring 212 will hold the high clutch element 210 disengagedwhen the low clutch element 268 yis engaged.`

Rotation of valve lowratio position of Fig. 6 to a high ratio position (not shown) connects the pressure source 2 I8 tothe high clutch line 2I'3 and connects the low clutch line 2I5 to the drain 200. Thus, in the high ratio position of Valve 306 pressure uid i's""admitted to chamber 216 to engage the trans- :mission in high gear ratio and the low clutch chamber 214 is connected `to drain, permitting spring 212 to disengage the low clutch.

and 2I3 are connected to drain 200. Inv the high Speed ratio position of valve 306 thelines 94 and 2I5, and consequently branch line 3I0, are connec'ted todrain 200, and there will be little or no pressure therein; the high clutch lines I 30, 2I3

are= connected to source 2I8 and consequently contaniiuid under pressure.

The ignition timing operating unit in Fig. 6 is exactlythe sameas described above in connection with Fig. 1. The valve piston |90 and the cylinder of the spark advance controlunit in. Fig. 6 are also-exactly the same as thel corresponding parts of the control unit described above in con- .nection with Fig. 1, but the actuating means for the-valve piston has been modified according to the embodiment of Fig. 6 in order to utilize supercharger pressure riseas a control means as well as an actuating means for the operating unit and so as tou enable the control unit, if desired, tobe compensated for changes in the speed ratio ofthe supercharger drive, resulting from actuation of the selector valve handle 308. I

In Figp diaphragm |86 of the control unit is spectively 'connected to supercharger rim `(or out- 306 byhandle 308 froml thei let''byfcondnitsll 1'4'5'- I 83'vian'd supercharger ythroat (or 'in-letif by' conduits :I1 Gil |8551 conduits# I 14," |16A are'alsoconn'ected'tothe' cylinder I 80iin tlieimfari'`- ner described in connection with Fig. 1.

Diaphragn'rY |86is biased-to theA right, urging valve-piston |90''t'o its rightdhand'position, bythe spring 2065 and' thi s"sprir`rg' is supported` atlits, left hand end-by a^movablewabutment v209, the position^of v'Wl'iich'determines the"pre-=loador"t'he datum'frceof-the'spring'2065. Y

'Abntment 209iis-connect-'ed'fto a-piston^rod 2II having on its left'hand/end a ypiston '2| 1 which'fref ciprocates irre` cylinder 2I`0'? Aspring 22| 'urges' piston-2H and-'abutment 20'9`to the'left; Rod f2`|'|` is separate from the' stern" I 88 "of the'valv'e piston' |90 vand consequently'the'valve'jpiston operates independently of the diaphragm" springA loading piston 211; the'pi's'ton 2 I1 and'abutmentf20i9serve merely to Ychange the lforceexertedby'spring'2.06"' on ,.the diaphragm |86A asLthe abutinentg209is movedi'to the right: or to .theieft 'in :response to changes in the fluidpressure admitted,'to the; cylinder` 2 I 9 'through' 'the branch.' conduit 3I0'.' In th'eembodinrient` of the invention rselected'jo'r. illustration ,in Fig- 6, this branch conduitis connected vto the conduit 2I5of the supercharger drive so` thatWhen the transmission is engaged. in` the low speed'ratio ui'dpressure frorn line A215 is-adrnittedjbyconduit 3l|0to the cyl-inder'Z'lS. forcingpiston 2I1 andabutment 209'1to. ytheright (to, aposition determined `:by stop 223()- against the-.forceofspring 21|-. Thisfcauses, the abut? ment .to compress diaphragm spring.,206 and. in.- creases the spring force urging valve pistonmIQIlf, to. fits. .right .l handpostion.. However, it.` ishtol-be understood that, it iswithinthe. scopeofthe in..- vention to. connect. branch. conduit.3l0,toconduit, 2| 3 '.-instead of ,conduit 215, .Whichtmayibe .prefers-1 able in somey installations where itis .desredpto increase the. loading.: on spring' 206'. when ther transmission .isin the yhigh-gspeed .ratioyfrather'i thanthe-low speedratio.t

Ire-Fig.4 6s valve-pistoni` |905 willvvbef-.maintaineda in its right hand., position@ by the spring l208' when4 the :pressure d-iiferenceabetween conduits I-14-,.E |116 is below aepr'edetermined rvalue. In this position-x conduit` I1'41is,connected to conduit \|'16-i 'andsconsduit l |116k ist` connected tofconduitf' |145, inst'lzthefiA same asv inFigol. However, it fwil'lbe notedthati the connections between conrzluitsrfl [14": 'and' |162' and ythepchamber.A I 10x-of4 -,ther;operatingeunit.: are; reverseding; Fig.: 6! (as';compared:;:withxEig; 1).,A consequently .im :Figli (inthe diaphragm; :.|;12`::o thiefy operating will' Jbe.' urged downwardly' to the f spark.` advancedvposition vby the;'pressureifdi-ffer.`v en'cezbetiveen thetri'rman'dfthroat lines; |149' |105 when the valve pistonnlQll-.i'siinzzitsarightshandfi position:`

When. the :valve piston il 30 5: is-in' .the f lft: handi* positionconduit 1421's connected-toy conduit- ITM' and conduit 'I 16 .is',connected: '-tocon'duit |104? andi' the pressure differencecbetween rim, :andfithroatn lines |14;` ITS'Lwillbe exe'rted'lacross diaphragm.: I1'21inA adirection urging;theloperatingfdiaphragmi\ 65 and` z valve. |62 i upwardly 'to r the .f Spanic: retarded-i position;

Operation. of Fig. Under idling: engine power.-fconditionsf-` or.. for'.

the-:valve piston` |190?` in its -,right fhandapositionn and supercharger-r riml or :outlet 'pressure` israele mitted. .to thefcharnber ron the y ,Aupperf-sidefeof operating diaphragm' ,|12 :and superchangerfthroati ominlea 'pressure is :admitted tafthemhambemonw. P

8 t'l'e'f `r lowem sidez off' tliis'-I diaphragm. Hiwe'ivex",F under these "conditions 'the superchargenpressnre riseis" 'noti large enough; to ``overcoIr-I-e the frceio'- spring |10;v andthesprnge holds -thewdi`aphragm |'12-' and"valvef IGZ'intheir upper'ior sparlifretardedf' position'. As theengi'ne power'is increasedfsuper" charger' pressure' risel also increases' and when' engine power' exceeds`-` a predetermined approxiy mate value (preferablyjust below or in the lower portion of the. cruising power range) the superchargerrpressurexrise'becomes sufficiently 'large'to compressv spring' |,185rand move' valve '|62'dow'n' wardly, thus advancing the'4 ignition timings Further increases in" engin'evpowerf and' super-f chargerl pressure rise" tend to maintain*'thefsparki advanced,4 untilVA a largeA4 enough' pressure"rise1 isA created by the supercharger betweenline'sfl1'4'j", I'16ff to move diaphragm-|86 ofithecontroliurrit' to the 'left against the force'of spring 206 there'- by'shifting'va'lv'e piston |'90"to' its 'extremedeft" hand position. When'this shift' occurs thereon"- nections betweenv lines'l14',j |16 andlines' |18, |14 are' reversed 'so thatv supercharger' rim pressure is" applied' on' the bottom of' diaphragml |12? and supercharger throat pressure, is' applied ion" ther topofthe diaphragm. The resultant' :'changein the' direction.' of :the uidLpressure force' across' diaphragm |12.:- aided :by'the force .of spring' |18," shiftsjvalve I62"to its'upperposition and'res'ult's in' changing the ignitiontiming toiretarded'posiition.

This 'sequence'.'of events occursy regardless of'. the position of 'the'sp'eed selector valve 205"and;' piston' 2'I1 andv .abutment 209L I-Ioxvever,V when; thef'branch" conduit' 3 .|0,is connected to low ratio?v linev 215;'. as shown, and the speed lsel'ectorrvalve' andnthe 'supercharger drive are in' the.4 lowAv gear" ratio, in'whi'ch' clutch 268is.engag,ed,uid pressure .is admittedby,conditt310 tothe cylinder'. 2 I9. and the abutment' 209'jwil1. .be' movedito,.or4 maintained in its. righ'thand position in Which'the. ppeloadon the,spring-2II6` vis increased to arela. tively high' value.. Under this' condition a, lrelaf tivelyw large val-11e of vsuperchargerY pressure;,rise willb'e require,d1jto move the valve piston |901' to. theV left.' This same result. maybe .producedwhen the ...transrnLs'sionisL in v.the ,high gear. ratio. (with,J cl utch..210 'engagedi by connectingbrancli .con-v` duit. ,3 |10 .tohigh .ratio .conduit 2 I3, insteadnflow'. ratio conduit 2'I`5Iv When branch conduit 3I0 is connected to lcon- A duit 2|5, as showniiin Fig: G-andfwhen the speed selector valve. andA the? supercharger drive arerin the..;.high. gear.. ratio, 1ines 2J5 .andI 310 araccm nectedtodlrainand thespring;22 I will holdpistone 2 I 1..and.abutment 200 in- ,the-.left .hand position-.t Under these conditions spring 206.is:preloaded.rtoia relativelyflow avalue. thusenahlingediaphragm |86v :"to th'eevalve'fpiston |90! toathe'fleit iat t a? relatively 'low valuaof. f superchargenpressurefi. rise. l l Thea-tendency fotI the engine to detonai'ie:isvina:A cr-reasednloy.` an'iincreasef inthef'temp'eratnre mfftheif chargingluid, `,such as: usuallyi resultspfrom lans, increase-infiimpellerf'speed-z it i. isnalso` increaseds byg'an@ advance in@ f. ignition timingay Thereforef: when 'atheffimpellerr is i being. driven. inV highr: geen: ratio it.may-be,desirab1e infsomerinstallatinnsr tof'retard-,the:timingrwvhenr supercharger pressure-.r risefreaches azwaluexwhichsfis 'lower'ftham thezrse'f; at which thevtiming'fzisfrshiftedifrom aduancetoz; retardmwith; low `impeller speed'ff-ratiof operation. Thefzfor-m "of: ith'e inventonfshownv-inr Figi; rautoa maticallyjfaccomplishes vthis 'resultf Jto some:.fdei'-:- gneei; because aeshift, :in rtransmissionsrattorfmmo low to high speed results in an increase in the pressure rise across the supercharger, other factors remaining constant. In addition, the piston 2l i may be actuated as described above by either high or low ratio clutch pressure so as to automatically provide additional compensation or adjustment of the control unit in accordance with a change in the speed of the impeller relative to the engine.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other ways without departure from its spirit as defined by the following claims.

I claim:

1. In an aircraft engine having a supercharger and an ignition system, a device for advancing and retarding the timing of said ignition system, means for subjecting said device to the pressure rise across said supercharger in a sense such as to advance said timing, and means for subjecting said device to the pressure rise across said supercharger in the opposite sense so as to retard said timing.

2. An ignition timing system for an engine having a supercharger, comprising, means for causing the pressure rise directly across said supercharger to advance the ignition timing of said engine upon an increase in said pressure rise to a first predetermined value, and means for causing said pressure rise to retard the ignition timing of said engine upon a further increase in said pressure rise to a second predetermined value.

3. A system according to claim 2, including a multi-speed gear transmission for driving said supercharger by said engine, and means for automatically changing said second predetermined value at which said timing is retarded in accordance with changes in the speed ratio of said transmission.

4. In an ignition timing system for an engine having a supercharger and a diaphragm for changing the ignition timing of said engine, a rst pair of conduits connected across said supercharger, a second pair of conduits connected across said diaphragm, and a fluid pressure respon-sive valve for connecting said second pair of c-onduits with said rst pair of conduits in either of two reversed positions.

5. Apparatus according to claim 4, in which said valve is responsive to a uid pressure which varies as a function of the engine intake airflow.

6. Apparatus according to claim 4, in which said valve is responsive to the pressure rise across said supercharger.

7. In a control apparatus for an engine having a supercharger and a device for changing an operating characteristic of said engine, means including a valve for applying the pressure rise across supercharger to said device in either of two opposite senses, said valve being movable to a, first position in which said pressure rise is applied to said device in a sense such as to vary said operating characteristic in a given direction and being movable to a second position in which said pressure rise is applied to said device in the opposite sense so as to vary said operating characteristic in the opposite direction, and means responsive to changes in the rate of flow of engine intake air for moving said valve between said rst and second positions.

8. In a control apparatus for an engine having a supercharger and a device for changing an operating characteri-stic of said engine, means including a valve for applying the pressure rise across said supercharger to said device in either of two opposite senses, said valve being movable to a first position in which said pressure rise i-s applied to said device in a sense such as to vary said operating characteristic in a. given direction and being movable to a second position in which said pressure rise is applied to said device in the opposite sense so as to vary said operating characteristic in the opposite direction, and means responsive to changes in the pressure rise across said supercharger for moving said valve between said rst and second positions.

PERRY W. PRATT.

REFERENCES CITED UNITED STATES PATENTS Name Date Jarvis Aug. '7, 1945 Number Certificate of Correction Patent No. 2,448,003. August 24, 1948.

PERRY W. PRATT It is hereby certied that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 10, line 11, claim 7, before the Word supercharger insert said; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Oce.

Signed and sealed this 9th day of November, A. D. 1948.

[SEAL] THOMAS F. MURPHY,

Assistant UOmmzsSz'o/nar of Patents. 

